Today, TV channels which are utilizing broadcasting satellites (BS) in Japan include BS-5 channel (Japan Satellite Broadcasting), BS-7 channel (NHK (Japan Broadcasting System)), and BS-11 channel (NHK). Also, TV programs and music programs using communications satellites (CS) have just begun in Japan.
In order to enjoy a TV program of a BS broadcast or a music program of a CS broadcast, a dedicated reception system is needed. For example, a satellite broadcast reception system for receiving BS broadcasts consists essentially of a BS antenna, a BS converter, and a BS tuner. The BS antenna efficiently gathers feeble electromagnetic waves from satellites and supplies them to the BS converter. Parabolic antennas are extensively used in civil applications. The BS converter amplifies signals in 12 GHz band received by the BS antenna and converts them into signals in 1 GHz band. The BS tuner selects the signal of the desired channel from the output signal from the BS converter, subjects the signal of the selected channel to signal processing (e.g., AGC (automatic gain control), IF amplification, FM demodulation, deamphasis, and energy dispersion-and-removal), and produces a picture signal and a sound signal. The picture and sound signals obtained from the BS tuner in this way are supplied to the BS tuner. Thus, programs of the BS broadcasts can be watched. Also, TV receivers incorporating a BS tuner are commercially available.
In BS and CS broadcasts, the viewer cannot directly enjoy some of the programs of the channel selected by the BS tuner described above. Examples are high-definition TV programs broadcast in certain time zones in BS-11 channel (in Japan), pay broadcast programs in BS-5 channel, and pay CS broadcast programs.
More specifically, the high-definition TV program is being broadcast, using a so-called MUSE signal. For pay broadcast programs, picture signals and sound signals are scrambled. Therefore, in order to watch the high-definition broadcast program, a MUSE decoder for decoding the MUSE signal and a down-converter for converting the high-definition picture signal from the MUSE decoder into a picture signal conforming to the NTSC standards are needed. The MUSE decoder and the down-converter are hereinafter collectively referred to as the MUSE down-converter. In order to watch pay broadcast programs, a descrambler (hereinafter referred to as the decoder) is necessitated.
In particular, to enjoy the high-definition broadcast program, the BS tuner is tuned to BS-11 channel, for example. The signal of the selected channel is supplied to the external MUSE down-converter connected with this TV receiver. Then, the signal from the MUSE down-converter which conforms to the NTSC standards is required to be fed back to the BS TV receiver. In order to watch pay broadcast programs, the BS tuner is tuned to BS-5 channel, for example. The signal of the selected channel is supplied to the external decoder. The descrambled signal from the decoder must be furnished back to the BS TV receiver.
Usually, the above-described MUSE down-converter and decoder are supplied as adaptors which are connected with BS tuners or TV receivers incorporating a BS tuner in order that only viewers who want get the devices, connect them to the tuners or TV receivers, and use them.
The BS converter is generally installed close to the BS antenna. For a BS broadcast reception system for an individual viewer, the BS converter is supplied with electric power from the BS tuner to power the converter. For a BS broadcast reception system for a group of users, the common BS converter is supplied with electric power from a dedicated power supply to power the converter. Accordingly, a commercially available BS tuner or TV receiver having a BS tuner has a power supply circuit capable of switching on and off the power supply for the BS converter. In this way, the tuners and receivers can be used for both types of reception system.
In order for the BS reception system to obtain high picture quality in receiving a broadcast program, it is necessary that the BS broadcast signal received via the BS antenna be in excess of a given level. Commercially available BS tuners and TV receivers having a BS tuner are capable of detecting the level of the BS broadcast signal and displaying it as the antenna level. This function of displaying the antenna level can also be used to adjust the orientation of the BS antenna when it is installed. That is, BS antennas generally are highly unidirectional to secure high gain. Therefore, when the antenna is installed, it is necessary to accurately adjust the angle to the broadcasting satellite. The angle is adjusted by making use of the above-described function of displaying the antenna level, to accomplish the maximum antenna level.
As described previously, the conventional television receiver having a BS tuner has a power supply circuit capable of switching on and off the power supply for the BS converter so that the receiver can be employed for both kinds of satellite broadcast reception system, i.e., for an individual user and for a group of users. Where the TV receiver is used for a BS broadcast reception system for an individual user, if the electric power from the power supply circuit that powers the BS converter is cut off by erroneously setting the condition of the switch of the power supply circuit, then it is impossible to receive satellite broadcasts. Since the condition of this switch of the power supply circuit is set only once upon connection with the BS converter, the switch is installed on the rear surface of the apparatus. Hence, it is difficult to check the condition of the switch. Furthermore, if it is operated incorrectly, the incorrect operation often remains unnoticed. PG,6